--- I'm inlining snippets of code from plat-mac/
bgenlocations.py ---
if sys.platform == 'mac':
    # For MacPython we know where it is
    def _pardir(p): return os.path.split(p)[0]
    BGENDIR=os.path.join(sys.prefix, "Tools", "bgen", 
"bgen")
else:
    # for unix-Python we don't know, please set it yourself.
    BGENDIR="/Users/jack/src/python/Tools/bgen/bgen"

With unix python using Jack's 2.3rc2 installer, BGENDIR 
should be /Applications/MacPython-2.3/Extras/Tools/bgen

#
# Where to put the python definitions files. Note that, on 
unix-Python,
# if you want to commit your changes to the CVS repository 
this should refer to
# your source directory, not your installed directory.
#
if sys.platform == 'mac':
    TOOLBOXDIR=os.path.join(sys.prefix, "Lib", "plat-mac", 
"Carbon")
else:
    TOOLBOXDIR="/Users/jack/src/python/Lib/plat-mac/
Carbon"

TOOLBOXDIR should point somewhere reasonable.  maybe 
os.path.expanduser('~/src/python/')... You should be able to 
override this without editing your python installation.  For 
example, it could print a warning instead of raising an 
exception.. look somewhere in sys.path for an override file, 
etc.

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user_id=45365

Sort-of a duplicate of #870997.